The present invention relates to a burglarproof system applied to doors of automotive vehicles.
Each door of an automotive vehicle is provided with a latching mechanism for maintaining the door closed. The latching mechanism is brought to an unlatched state by unlatching operating means such as a door handle or the like, to permit the door to be opened. Moreover, the door is provided with a locking mechanism associated with the latching mechanism, for preventing various equipments within the automotive vehicle and the automotive vehicle per se from being stolen. The locking mechanism is also associated with a door key cylinder, and is movable between a locked position and an unlocked position by turning of a key inserted into the door key cylinder. In the locked position, the locking mechanism prohibits operating force acting on the door handle from being transmitted to the latching mechanism, whereby the door cannot be opened. In the unlocked position, the operating force acting on the door handle is transmitted to the latching mechanism, so that the door can be opened.
However, even if the door is provided with the locking mechanism, a habitual thief can bring the locking mechanism to the unlocked position without relying upon operation of the key. That is, the habitual thief forms a bore in a part of the window glass, and operates a lock button arranged at the door and located adjacent a lower edge of the window on the inside of the vehicle, whereby the habitual thief can bring the locking mechanism to the unlocked position. Alternatively, a thin and elongated element is inserted through a slit formed between the window frame of the door and an edge of the window glass slidable within the window frame, and the locking mechanism can be brought to the unlocked position by the forward end of the thin and elongated element
In view of the above circumstances, a burglarproof system has been developed, as disclosed in Japanese Patent Application Laid-Open No. 61-71252, which comprises a door key switch for detecting insertion of a key with into a door key cylinder, a door lock switch for detecting in which one of locked and unlocked positions a locking mechanism is, and a stealing detection circuit. Judgment by the stealing detection circuit indicates stealing, when the stealing detecting circuit does not receive a key-insertion detection signal from the door key switch, but receives an unlocking detection signal from the door lock switch, whereby the stealing detection circuit outputs a stealing detection signal. In response to the stealing detection signal, the horn is sounded, or the engine start-up is prohibited, thereby preventing stealing.
By the way, a regular driver of the automotive vehicle inserts the key into the door key cylinder and turns the key, thereby bringing the locking mechanism to the unlocked position. At this time, the stealing detection circuit receives the unlocking detecting signal from the door lock switch, and also receives the key-insertion detection signal from the door key switch, so that the stealing detection circuit does not output the stealing detection signal.
With the system disclosed in the Japanese patent, however, the door key switch is arranged adjacent the innermost end of the key cylinder remote from the key insertion opening, and the forward end of the key inserted pushes the door key switch, thereby obtaining the key-insertion detection signal. Because of such arrangement, mere insertion of an elongated element, in place of the key, into the door key cylinder by a thief enables the key-insertion detection signal to be issued. Even if the locking mechanism is unlocked after the issuance of the key-insertion detection signal, the stealing detection circuit does not output the stealing detection signal. Thus, it has been impossible to secure prevention of stealing.